Helicobacter pylori γ-glutamyl transpeptidase:A formidable virulence factor

Helicobacter pylori(H.pylori)produce an enzyme known asγ-glutamyl transpeptidase(HpGGT)that is highly conserved and common to all strains.HpGGT has been gaining increasing attention as an important virulence factor of the bacterium,having been demonstrated to be an important colonization factor in several animal models and has also recently been strongly associated with the development of peptic ulcer disease.From the results of various independent researcher groups,it is clear that HpGGT acts through several pathways to damage gastric epithelial cells including the induction of apoptosis and cell cycle arrest,production of reactive oxygen species leading to DNA damage,promotion of inflammation by increasing cyclooxygenase-2 and interleukin-8 expression,and upregulation of heparin-binding epidermal growth factor-like growth factor resulting in cell survival and proliferation.In addition,the potential role of HpGGT in promoting gastric carcinogenesis will also be discussed in this review.Apart from affecting the gastric epithelium,HpGGT also has immunomodulatory actions on host immune cells where it displays an antiproliferative effect on T cells by inducing cell cycle arrest and also works with other H.pylori virulence factors to skew dendritic cells towards a tolerogenic phenotype,possibly contributing to the persistence of the pathogen in the gastric mucosa.

Agglutination of Helicobacter pylori coccoids by lectins

AIM To study the agglutination pattern ofHelicobacter pylori coccoid and spiral forms.METHODS Assays of agglutination andagglutination inhibition were applied usingfifteen commercial lectins.RESULTS Strong agglutination was observedwith mannose-specific Concanavalin A(Con A),fucose-specific Tetragonolobus purpureas(Lotus A)and N-acetyl glucosamine-specificTriticum vulgaris(WGA)lectins.Mannose andfucose specific lectins were reactive with allstrains of H.pylori coccoids as compared to thespirals.Specific carbohydrates,glycoproteinsand mucin were shown to inhibit H.pylorilectin-agglutination reactions.Pre-treatment ofthe bacterial cells with formalin and sulphuricacid did not alter the agglutination patterns withlectins.However,sodium periodate treatment ofbacterial cells were shown to inhibitagglutination reaction with Con A,Lotus A andWGA lectins.On the contrary,enzymatictreatment of coccoids and spirals did not showmarked inhibition of H.pylori-lectinagglutination.Interestingly,heating of H.pylori cells at 60℃ for 1 hour was shown toaugment the agglutination with all of the lectinstested.CONCLUSION The considerable differences inlectin agglutination patterns seen among the twodifferentiated forms of H.pylori might beattributable to the structural changes during theevents of morphological transformation,resulting in exposing or masking some of the sugar residues on the cell surface.Possibility ofvarious sugar residues on the cell wall of thecoccoids may allow them to bind to differentcarbohydrate receptors on gastric mucus andepithelial cells.The coccoids with adherencecharacteristics like the spirals could aid in thepathogenic process of Helicobacter infection.This may probably lead to different clinicaloutcome of H.pylori associated gastroduodenaldisease.

Effect of biopsies on sensitivity and specificity of ultra-rapid urease test for detection of Helicobacter pylori infection:A prospective evaluation

AIM:To prospectively assess the sensitivity,specificity and time to positivity of theUltra-rapid urease test (URUT) for Helicobacter pylori(H pylori),and compare the results of one with those of two biopsies. METHODS:Five antral biopsies were taken in consecutive patients undergoing upper endoscopy:one and two biopsies for URUT,and one each for H pylori culture and histology. URUT was read at 1,5,10,20 and 30 min,1,2,3 and 24 h after biopsy insertion into the reagent.A positive histology and/or culture was used as positive reference“gold standards”. RESULTS:URUT was more sensitive for detecting Hpylori with two biopsies rather than one,at all time points up to 120 min.The sensitivity improved from 3.6% to 82.1% for one biopsy and 10.7% to 85.7% for two biopsies from 1 to 120 min.The sensitivity reached 96.4% at 24 h for both, but the specificity reduced from 100% to 96% and 92% for one and two biopsies,respectively. CONCLUSION:Development of a positive URUT result is hastened by doubling the number of gastric biopsies.We recommend taking two instead of one biopsy to achieve an earlier positive URUT result so that H pylori eradication therapy can be initiated before patient is discharged from the endoscopy suite.

Prominent role of y-glutamyl-transpeptidase on the growth of Helicobacter pylori

AIM: γ-glutamyl transpeptidase (GGT) has been reported as a virulence and colonizing factor of Helicobacter pylori (Hpylori). This study examined the effect of GGT on thegrowth of H pylori. METHODS: Standard H pylori strain NCTC 11637 and 4 dinical isolates with different levels of GGT activity as measured by an enzymatic assay were used in this study. Growth inhibilJon and stimulation studies were carried out by culturing H pyloriin brain heart infusion broth supplemented with specific GGT inhibitor (L-serine sodium borate complex, SBC) or enhancer (glutathione together with glycyl-glycine), respectively. The growth profiles of Hpyloriwere determined based on viable bacterial count at time interval. RESULTS: Growth was more profuse for Hpyloriisolates with higher GGT activity than those present with lower GGT activity. However, in the presence of SBC, growth of Hpylori was retarded in a dose dependent manner (P = 0.034). In contrast, higher growth rate was observed when GGT activity was enhanced in the presence of glutathione and glycyl-glycine. CONCLUSION: Higher GGT activity provides an advantage to the growth of Hpy/oriin vitro. Inhibition of GGT activity by SBC resulted in growth retardation. The study shows that GGT plays an important role on the growth of Hpy/ori.

Validation of four Helicobacter pylori rapid blood tests in a multi-ethnic Asian population

AIM: To validate the accuracy of four rapid blood tests in the diagnosis of Helicobacter pylori.METHODS: Consecutive dyspeptic patients scheduled for endoscopy at the National University Hospital,Singapore, were interviewed and had blood drawn for serology. The first 109 patients were tested with BM-test (BM), Pyloriset Screen (PS) and QuickVue (QV), and the next 99 subjects were tested with PS and Unigold (UG).Endoscopies were performed blinded to rapid blood test results and biopsies were taken for culture and rapid urease test. Urea breath tests were performed after endoscopies. The rapid blood test results were compared with four reference tests (rapid urease test, culture,serology, and breath test).RESULTS: The study population composed of 208patients (mean age 43.1 years; range 18-73 years; 119males; 174 Chinese). The number of evaluable patientsfor BM, QV, UG and PS were 102, 102, 95, and 197,respectively. The sensitivity and specificity, respectively were: PS 80.2%, 95.8%; UG 55.9%, 100%; QV 43.3%,100%; BM 67.2%, 97.1%.CONCLUSION: The rapid blood test kits showed high specificity and positive predictive value (97-100%), while sensitivity and negative predictive value ranged widely (43%-80% and 47%-73%, respectively). Among test kits, PS showed the best sensitivity (80%), best negative predictive value (73%) and best negative likelihood ratio (0.207). PS had a specificity of 96%, positive predictive value of 97% and positive likelihood ratio of 19.1.

The Molecular Mechanism of Interaction between Sushi Peptide and Pseudomonas Endotoxin

Septic shock is caused by Gram-negative bacterial infection. Lipopolysaccharide （LPS） is the bioactive molecule present on the outer membrane of the Gram-negative bacteria. It is generally thought that LPS interacts with sensors on the host cell membrane to activate the intracellular signaling pathway resulting in the overproduction of cytokines such as TNF-α This causes inflammation and ultimately, septic shock. Lipid A is the pharmacophore of the LPS molecule. Thus, developing bio-molecules which are capable of binding LPS at high affinity, especially to the lipid A moiety is an efficient way to neutralize the LPS toxicity. Factor C, a serine protease in the horseshoe crab ameobocytes, is sensitive to trace levels of LPS. We have derived Sushi peptides from the LPS-binding domains of Factor C. Our earlier study showed that the Sushi peptides inhibit LPS-induced septic shock in mice. Here, we demonstrate that the molecular interaction between LPS and Sushi 1 peptide is supported by the hydrophobic interaction between the lipid tail of LPS and Sushi 1 peptide. Furthermore, in the presence of LPS, the peptide transitions from a random structure into an α-helical conformation and it disrupts LPS aggregates, hence, neutralizing the LPS toxicity.